Active exhaust-noise attenuation muffler

ABSTRACT

An active exhaust-noise attenuation muffler for an exhaust pipe includes a control unit, a sensor assembly which is operatively connected to the control unit, and a gas-tight diaphragm constructed to be resistant to exhaust gas in the exhaust pipe and acoustically coupled with a flow of exhaust gas in the exhaust pipe. The diaphragm has a surface which confronts the exhaust gas. A transducer is operated by the control unit for causing the surface of the diaphragm to vibrate in a bending vibration mode to produce a structure-borne sound in dependence on exhaust noise.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application,Serial No. 10 2005 011 747.3, filed Mar. 11, 2005, pursuant to 35 U.S.C.119(a)-(d), the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates, in general, to an active exhaust-noiseattenuation muffler for exhaust pipes.

Nothing in the following discussion of the state of the art is to beconstrued as an admission of prior art.

Exhaust systems of motor vehicles typically include an exhaust-noiseattenuation muffler to reduce the intensity of exhaust noise generatedby the motor to an acceptable level. The sound pressure level may amountup to 160 dB(A). Regulations provide hereby a legal standard for noisereduction.

Passive mufflers operate on the basis of sound absorption and includefibrous or open-pored materials having large and greatly structuredsurfaces. In this way, exhaust noise is diverted and reflected inabsorbing and sound-suppressing mazes so that the noise energy isreduced until the exhaust noise drops below a desired level. These typesof passive exhaust-noise attenuation mufflers retain exhaust gas so thatengine performance is adversely affected. Other types of exhaust-noiseattenuation mufflers operate on the utilization of a countersound tosuperpose on the disturbing noise with a compensation sound having asame frequency and intensity as the disturbing noise but beingphase-shifted by 180°. As a result of the interference, the disturbingnoise is attenuated. Countersound may be produced passively byparticularly constructed resonators and actively by loudspeakers.Resonators may be configured as λ/4 pipe and coupled to the side of theexhaust pipes. Sound is reflected phase-shifted by 180° at the end ofthe λ/4 pipe. Reflecting sound waves superpose on the disturbing noiseto effect the noise attenuation. As a consequence of the time that isrequired for the sound to travel twice along the length of the λ/4 pipeand due to dynamic conditions that result in a change in frequency ofthe exhaust noise in the exhaust pipe, the superimposition with thereflected sound fails to realize the desired compensation. Moreover, thefrequencies where complete suppression is possible are limited to amultiple of λ/4 for physical reasons.

In view of these limitations, the use of active exhaust-noiseattenuation mufflers has been developed which are equipped with asecondary sound source to produce a compensation sound by means ofloudspeakers. For purposes of generating the compensation sound, controlcircuits and closed loops have been used. The control circuits includesensors to ascertain relevant parameter for the exhaust noise, like e.g.motor speed, load state of the motor, exhaust temperature. A controlunit generates output signals in response to incoming input signals tooperate the loudspeaker disposed on the exhaust pipe. The use of aclosed loop is able to further enhance sound reduction by complementingthe sensor assembly with a pressure sensor or microphone. In response tothe exhaust noise ascertained by the sensor assembly, the control unitis then able to generate jointly with the loudspeaker a compensationsound which is suited to the dynamic changes of the exhaust noise.

Establishing physical parameter in connection with reduction of exhaustnoise is very difficult. As noted above, exhaust noise may reach a soundpressure level of up to 160 dB(A), whereby the exhaust gas pulsates. Thetemperature of exhaust gas in the exhaust pipe may reach up to 600° C.so that the speed of sound rises from 330 m/s to 600 m/s. Moreover, theexhaust gas is chemically extremely aggressive.

Heretofore, the use of cone-type loudspeakers for exhaust noiseattenuation has proven unsatisfactory because these types ofloudspeakers are unable to withstand the encountered rough physicalconditions. In other words, the diaphragm and magnets wear off quickly.A proposal to use diaphragms of titanium has been discarded because ofthe prohibitively expensive costs for mass production. In order togenerate low frequencies, large-area diaphragms and heavy magnets arerequired which however are too bulky for installation in the availablespace in motor vehicles and unsuitable for large-scale production inview of their weight.

It would therefore be desirable and advantageous to provide an improvedactive exhaust-noise attenuation muffler which obviates prior artshortcomings and which is compact in structure and reliable in operationregardless of the type of vehicle involved.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an activeexhaust-noise attenuation muffler for an exhaust pipe includes a controlunit, a sensor assembly operatively connected to the control unit, agas-tight diaphragm constructed to be resistant to exhaust gas in theexhaust pipe and acoustically coupled with a flow of exhaust gas in theexhaust pipe, with the diaphragm having a surface which confronts theexhaust gas, and a transducer operated by the control unit for causingthe surface of the diaphragm to vibrate in a bending vibration mode toproduce a structure-borne sound in dependence on exhaust noise.

The present invention resolves prior art problems by superimposing theexhaust noise with the compensation sound of a loudspeaker whichoperates as electroacoustic transducer on the basis of bending waves.Loudspeakers of this type have a diaphragm with a surface on whichbending waves and shear waves can propagate when caused to vibrate by atransducer. The wave propagation in diaphragms may be realized in manyways. In thicker diaphragms, compact waves and dilatational waves aredominant, whereas thinner media have in addition bending and shearwaves. Excitation of bending waves has been shown suitable forapplication in loudspeakers in view of their amplitude and theirpropagation performance. The propagation performance of bending waves ina diaphragm is primarily impacted by the bending stiffness of thediaphragm, with the bending stiffness being frequency-dependent. In theso-called coincidence frequency, the phase velocity of the wave in thediaphragm matches the phase velocity in air. At this frequency, the waveseparates from the diaphragm at an angle of about 0°. Above thecoincidence frequency, the angle increases up to 90°, thereby abruptlyincreasing the efficiency. The coincidence frequency thus constitutesthe lowest frequency at which the bending waves can be converted intoair sound waves. Below this frequency, the diaphragm vibratespredominantly in a piston-like manner.

Loudspeakers of this type can be made flat. The diaphragm is thin andcan be made planar or slightly curved. A flat configuration of thediaphragm significantly simplifies a calculation of bending waves andthe overall configuration of the diaphragm. In addition, largerdiaphragms can be made more compact and may be disposed, for example, inclose proximity to the exhaust pipe at the bottom of the vehicle body.

According to another feature of the present invention, the transducercan be secured to the backside of the diaphragm and coupled therewith.The diaphragm may suitably held in a frame of the housing of theloudspeaker. Suitably, the housing is disposed on the exhaust-distalside of the diaphragm in surrounding relationship to the transducer.

According to another feature of the present invention, the diaphragm isconstructed to be able to withstand chemical and thermal impacts in theexhaust pipe. In addition, the diaphragm should be gastight.

The loudspeaker is operated by the control unit which is operativelyconnected to the sensor assembly via signal lines. The exhaust-noiseattenuation muffler can thus be constructed with a control circuit aswell as a closed loop in order to actively and efficiently reduceexhaust noise.

According to another feature of the present invention, the diaphragm maybe disposed in an opening in a wall of the exhaust pipe. As a result,the exhaust-noise attenuation muffler is compact and the loudspeaker canbe placed in close proximity of the exhaust pipe. As a result of thedirect linkage of the loudspeaker with the exhaust gas flow, attenuationis significantly simplified because fewer factors need to be taken intoaccount to generate the countersound. As an alternative, it may alsopossible to dispose a resonator in an opening in the wall of the exhaustpipe, wherein the diaphragm is operatively connected to the resonator ata distance to the opening. As a consequence of the distance to the pipe,the diaphragm is thermally decoupled from the flow of exhaust gas sothat the diaphragm undergoes less stress and thus can be constructedsimpler. Moreover, the resonator may be used to align the sound and tofocus the sound toward the exhaust gas flow.

According to another feature of the present invention, the diaphragm maybe configured to conform to a contour of a wall of the exhaust pipe,resulting in an arched configuration of the diaphragm. This slightcurving of the diaphragm allows easy integration in the exhaust pipe.Thus, the available installation space can be efficiently utilized.

According to another feature of the present invention, theexhaust-confronting surface of the diaphragm may be coated with metalthrough a vapor deposition process. In this way, the chemical resistanceand the temperature-resistance of the diaphragm can be significantlyenhanced. As an alternative, a stainless steel foil may be applied uponthe exhaust-confronting surface of the diaphragm.

The nature of the exhaust noise is substantially influenced by themotor, i.e. speed level and load state as well as by the temperature ofthe exhaust gas flow. Thus, it may be suitable to operatively connectthe control unit with an electronic motor control system. The directlink enables a continuous transmission of motor data during operation tothe control unit, without requiring complex signal conversion processingwith resultant decrease in efficiency and loss in time. Suitably,respective interfaces are provided at the output of the electronic motorcontrol system and at the input of the control unit.

According to another feature of the present invention, the sensorassembly may include a temperature sensor for measuring an exhausttemperature in the exhaust pipe. As the speed of sound is dependentespecially on the temperature of the exhaust, consideration of theexhaust temperature significantly enhances the efficiency of theexhaust-noise attenuation muffler.

According to another feature of the present invention, the sensorassembly may include a throttle sensor for determining a throttleposition. The arrangement of a throttle sensor provides inference aboutthe load state of the motor. Sensors of this type are typically used incurrent motor vehicles and their structure and operation are generallyknown to the artisan.

According to another feature of the present invention, the sensorassembly may include a speed sensor for determining a motor speed.

According to another feature of the present invention, the sensorassembly may include a pressure sensor, e.g. a microphone, fordetermining the exhaust noise in the exhaust pipe. Provision of a closedloop for producing the compensation sound is especially effective toattenuate exhaust noise. The sensor assembly is hereby resistant to theexhaust gas like the loudspeaker.

According to another feature of the present invention, a microprocessormay be provided for control of the control unit. This affordsflexibility to adapt the exhaust-noise attenuation muffler to varioussituations at hand. The control performance of the control unit isprogram-controlled. The programs may be modified or exchanged via arespective interface on the control unit. In this way, exhaust noise canbe configured like a sound design. A microprocessor-controlled controlunit further simplifies the installation of the exhaust-noiseattenuation muffler independent from the motor vehicle because it isonly required to suit the software while the hardware can remain thesame.

According to another feature of the present invention, the control unitmay be constructed to allow adjustment of the control performance. As aresult, the operator is able at any time to directly influence the noiseof the vehicle by actuating switches or variable transformers. In otherwords, the noise can be adjusted by the operator to sound especiallyracy or gentle.

According to another feature of the present invention, the transducermay be constructed as an oscillation coil. Use of an oscillation coilresults in a compact configuration and arrangement of few moving parts.As an alternative, the transducer may include an electric motor having adriveshaft, with an eccentric secured to the driveshaft and coupled tothe diaphragm via a connecting rod. In this way, the frequency of thevibrating diaphragm can be adjusted in an especially easy and robustmanner. The electric motor may be placed separate and away from theexhaust gas flow, thereby decreasing the exposure of the transducer tothermal stress. In the event, the transducer is intended for securementdirectly to the diaphragm, it is suitable to construct the transducerheat-resistant.

According to another feature of the present invention, a housing may beprovided for accommodating the diaphragm and the transducer. Theprovision of a housing serves two purposes, namely as protection fromthe environment, and facilitation of the assembly because the transducertogether with the diaphragm and the housing can be constructed as aprefabricated unitary structure that can be shipped as a unit forassembly.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be morereadily apparent upon reading the following description of currentlypreferred exemplified embodiments of the invention with reference to theaccompanying drawing, in which:

FIG. 1 is a partial longitudinal section of a first embodiment of anactive exhaust-noise attenuation muffler according to the presentinvention;

FIG. 2 is a partial longitudinal section of a second embodiment of anactive exhaust-noise attenuation muffler according to the presentinvention;

FIG. 3 is an enlarged detailed view of a loudspeaker of the activeexhaust-noise attenuation muffler of FIGS. 1 and 2; and

FIG. 4 is an enlarged detailed view of a variation of a loudspeaker ofthe active exhaust-noise attenuation muffler according to the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements are generallyindicated by same reference numerals. These depicted embodiments are tobe understood as illustrative of the invention and not as limiting inany way. It should also be understood that the drawings are notnecessarily to scale and that the embodiments are sometimes illustratedby graphic symbols, phantom lines, diagrammatic representations andfragmentary views. In certain instances, details which are not necessaryfor an understanding of the present invention or which render otherdetails difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 1, there is showna partial longitudinal section of a first embodiment of an activeexhaust-noise attenuation muffler according to the present invention,generally designated by reference numeral 1, for an exhaust pipe 2 thatmay find application for example in a motor vehicle. The activeexhaust-noise attenuation muffler 1 is provided to superpose the noiseof the exhaust with a 180° phase-shifted compensation sound of aloudspeaker 3 so as to reduce or suppress the exhaust noise.

The loudspeaker 3 has a flat configuration and is paced in a lateralopening 4 in the wall 5 of the exhaust pipe 2 of an unillustrated motor.The loudspeaker 3 has a diaphragm 7 and a transducer which isimplemented by way of example in the form of an oscillation coil 8.Both, the diaphragm 7 and the oscillation coil 8 are arranged in ahousing 6. The diaphragm 7 is thin and made of several material layersso as to exhibit a particularly low coincidence frequency and a broadfrequency spectrum within which the diaphragm 7 is able to vibrate so asto generate a structure-borne sound. Resistance to the exhaust gas andtightness of the diaphragm 7 are ensured by vapor-depositing metal M onan exhaust-confronting side of the diaphragm 7, as also shown on anenlarged scale in FIG. 3. As an alternative to the vapor-deposition ofmetal, the application of a stainless steel foil 29 upon theexhaust-confronting surface of the diaphragm 7 is also conceivable, asshown in FIG. 4.

The diaphragm 7 is aligned in the opening 4 such that its surface 9contacts the exhaust gas flow AS. Secured to the backside of thediaphragm 7 is the oscillation coil 8 which, when excited, causes thediaphragm 7 to vibrate. As a result, bending waves are able to propagateon the exhaust-confronting surface 9 of the diaphragm 7. The oscillationcoil 8 is also made of heat-resistant material. The loudspeaker 3 hasenough potential to produce a compensation sound of necessary intensity.

The loudspeaker 3 is operated by a microprocessor-controlled controlunit 10 which is mounted in a vehicle body of the motor vehicle at aseparate location. The control unit 10 has various interfaces 11-16,with reference numeral 11 relating to an interface for an electronicmotor control system 20 forming part of a sensor assembly, referencenumeral 12 relating to an interface for data transfer, reference numeral13 relating to an interface for input of a microphone 22 forming anotherpart of the sensor assembly, reference numeral 14 relating to aninterface for a temperature sensor 21 forming yet another part of thesensor assembly, reference numeral 15 relating to an interface for avoltage supply, and reference numeral 16 relating to an interface for acontrol panel 17. In response to the signals transmitted by the sensorassembly via signal lines 27, the control unit 10 computes acompensation vibration which is converted by a digital-to-analogconverter 18 into an electric oscillation and boosted by an amplifier 19of the control unit 10 before being delivered to the loudspeaker 3.Computation of the compensation vibration is program-controlled, withthe programs being exchangeable via the data transfer interface 12. Eachvehicle type has its own particular program. The control performance ofthe control unit 10 may be modified by an operator using the controlpanel 17 in order to give the vehicle a racy or gentle sound or to makethe exhaust noise quieter or louder.

The control unit 10 is directly linked to the sensor assembly comprisedof the electronic motor control system 20, temperature sensor 21, andmicrophone 22, whereby the temperature sensor 21 and the microphone 22are mounted to the exhaust pipe 2. Signal transfer takes place via thesignal lines 27. The electronic motor control system 20 transmitsinformation about the speed and load state of the motor from aparticular output interface 23 to the control unit 10. The temperaturesensor 21 ascertains a temperature of the exhaust gas flow AS in theexhaust pipe 2 in close proximity of the loudspeaker 3 and isconstructed resistant to the exhaust gas. The microphone 22 is alsoconstructed resistant to the exhaust gas and disposed upstream of theloudspeaker 3 in an opening 24 in the wall 5 of the exhaust pipe 2.

In order to modify the sound of the vehicle, the driver uses theoperating panel 17 which is placed within easy reach of the driverduring travel. The operating panel 17 includes switches 25 and avariable transformer 26 and is linked to the control unit 10 via asignal line 27.

Referring now to FIG. 2, there is shown a partial longitudinal sectionof a second embodiment of an active exhaust-noise attenuation muffler 1according to the present invention. Parts corresponding with those inFIG. 1 are denoted by identical reference numerals and not explainedagain. The description below will center on the differences between theembodiments. In this embodiment, the loudspeaker 3 is secured to aresonator 28 which is placed in the lateral opening 4 in the wall 5 ofthe exhaust pipe 2. The resonator 28 has a funnel-shaped configurationand is made of sheet metal. The diaphragm 7 is disposed here at adistance A to the opening 4. A structure-borne sound produced by thediaphragm 7 propagates in the resonator 28 and superposes on the exhaustnoise in the exhaust pipe 2, after traveling through the opening 4.

While the invention has been illustrated and described in connectionwith currently preferred embodiments shown and described in detail, itis not intended to be limited to the details shown since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention. The embodiments werechosen and described in order to best explain the principles of theinvention and practical application to thereby enable a person skilledin the art to best utilize the invention and various embodiments withvarious modifications as are suited to the particular use contemplated.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims and includes equivalents of theelements recited therein:

1. An active exhaust-noise attenuation muffler for an exhaust pipe,comprising: a control unit; a sensor assembly operatively connected tothe control unit; a gas-tight diaphragm constructed to be resistant toexhaust gas in an exhaust pipe and acoustically coupled with a flow ofexhaust gas in the exhaust pipe, said diaphragm having a surface whichconfronts the exhaust gas; and a transducer operated by the control unitfor causing the surface of the diaphragm to vibrate in a bendingvibration mode to produce a structure-borne sound in dependence onexhaust noise.
 2. The exhaust-noise attenuation muffler of claim 1,wherein the diaphragm is disposed in an opening in a wall of the exhaustpipe.
 3. The exhaust-noise attenuation muffler of claim 1, furthercomprising a resonator received in an opening in a wall of the exhaustpipe, wherein the diaphragm is operatively connected to the resonator ata distance to the opening.
 4. The exhaust-noise attenuation muffler ofclaim 1, wherein the diaphragm is flat.
 5. The exhaust-noise attenuationmuffler of claim 1, wherein the diaphragm is configured to conform to acontour of a wall of the exhaust pipe.
 6. The exhaust-noise attenuationmuffler of claim 1, wherein the surface of the diaphragm is coated withmetal through a vapor deposition process.
 7. The exhaust-noiseattenuation muffler of claim 1, further comprising a stainless steelfoil applied upon the surface of the diaphragm.
 8. The exhaust-noiseattenuation muffler of claim 1, further comprising an electronic motorcontrol system operatively connected to the control unit.
 9. Theexhaust-noise attenuation muffler of claim 1, wherein the sensorassembly includes a temperature sensor for measuring a temperature ofthe exhaust gas in the exhaust pipe.
 10. The exhaust-noise attenuationmuffler of claim 1, wherein the sensor assembly includes a throttlesensor for determining a throttle position.
 11. The exhaust-noiseattenuation muffler of claim 1, wherein the sensor assembly includes aspeed sensor for determining a motor speed.
 12. The exhaust-noiseattenuation muffler of claim 1, wherein the sensor assembly includes apressure sensor for determining the exhaust noise in the exhaust pipe.13. The exhaust-noise attenuation muffler of claim 12, wherein thepressure sensor is a microphone.
 14. The exhaust-noise attenuationmuffler of claim 1, further comprising a microprocessor for controllingthe control unit.
 15. The exhaust-noise attenuation muffler of claim 1,wherein the control unit includes an amplifier for boosting a signalreceived from the sensor assembly.
 16. The exhaust-noise attenuationmuffler of claim 1, wherein the control unit is constructed to allowadjustment of a control performance.
 17. The exhaust-noise attenuationmuffler of claim 1, wherein the transducer is an oscillation coil. 18.The exhaust-noise attenuation muffler of claim 1, wherein the transduceris constructed to be heat-resistant.
 19. The exhaust-noise attenuationmuffler of claim 1, further comprising a housing for accommodating thediaphragm and the transducer.
 20. The exhaust-noise attenuation mufflerof claim 20, wherein the housing is disposed on an exhaust-distal sideof the diaphragm in surrounding relationship to the transducer.
 21. Theexhaust-noise attenuation muffler of claim 1, wherein the transducer issecured to a reverse side of the diaphragm.
 22. The exhaust-noiseattenuation muffler of claim 1, wherein the compensation sound is 180°phase-shifted to the exhaust noise.